Combination of hydrogen and pressure sensors

ABSTRACT

The invention provides a sensor assembly for determining the concentration of hydrogen in an insulating fluid in electric power generation, transmission, and distribution equipment. The assembly includes a housing having an opening therein communicating with the fluid, a hydrogen sensor disposed in the housing and responsive to the concentration of hydrogen in the fluid and generating a signal related to the concentration of hydrogen, and a pressure sensor disposed in the housing responsive to the fluid and generating a second signal indicative of the pressure of the fluid in the equipment. The assembly further includes a signal processor disposed in the housing and connected to the hydrogen sensor and the pressure sensor and responsive to the first and second signals for generating a third signal representing the concentration of hydrogen in the fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

FIELD OF THE INVENTION

This invention relates to the sensing of hydrogen in oils. Itparticularly relates to apparatus for sensing of hydrogen in electricpower generation transmission and distribution equipment oil.

BACKGROUND OF THE INVENTION

Electrical equipment, particularly medium-voltage or high-voltageelectrical equipment, requires a high degree of electrical and thermalinsulation between components thereof. Accordingly, it is well known toencapsulate components of electrical equipment, such as coils of atransformer, in a containment vessel and to fill the containment vesselwith a fluid. The fluid facilitates dissipation of heat generated by thecomponents and can be circulated through a heat exchanger to efficientlylower the operating temperature of the components. The fluid also servesas electrical insulation between components or to supplement other formsof insulation disposed around the components, such as cellulose paper orother insulating materials. Any fluid having the desired electrical andthermal properties can be used. Typically, electrical equipment isfilled with an oil, such as castor oil, mineral oil, or vegetable oil,or a synthetic “oil”, such as chlorinated diphenyl, silicone, or sulfurhexafluoride.

Often, electrical equipment is used in a mission-critical environment inwhich failure can be very expensive, or even catastrophic, because of aloss of electric power to critical systems. In addition, failure ofelectrical equipment ordinarily results in a great deal of damage to theequipment itself and surrounding equipment thus requiring replacement ofexpensive equipment. Further, such failure can cause injury to personneldue to electric shock, fire, or explosion. Therefore, it is desirable tomonitor the status of electrical equipment to predict potential failureof the equipment through detection of incipient faults and to takeremedial action through repair, replacement, or adjustment of operatingconditions of the equipment. However, the performance and behavior offluid-filled electrical equipment inherently degrades over time. Faultsand incipient faults should be distinguished from normal and acceptabledegradation.

A known method of monitoring the status of fluid-filled electricalequipment is to monitor various parameters of the fluid. For example,the temperature of the fluid and the total combustible gas (TCG) in thefluid is known to be indicative of the operating state of fluid-filledelectrical equipment. Therefore, monitoring these parameters of thefluid can provide an indication of any incipient faults in theequipment. For example, it has been found that carbon monoxide andcarbon dioxide increase in concentration with thermal aging anddegradation of cellulosic insulation in electrical equipment. Hydrogenand various hydrocarbons (and derivatives thereof such as acetylene andethylene) increase in concentration due to hot spots caused bycirculating currents and dielectric breakdown such as corona and arcing.Concentrations of oxygen and nitrogen indicate the quality of the gaspressurizing system employed in large equipment, such as transformers.Accordingly, “dissolved gas analysis” (DGA) has become a well-acceptedmethod of discerning incipient faults in fluid-filled electricequipment.

In conventional DGA methods, an amount of fluid is removed from thecontainment vessel of the equipment through a drain valve. The removedfluid is then subjected to testing for dissolved gas in a lab or byequipment in the field. This method of testing is referred to herein as“offline” DGA. Since the gases are generated by various known faults,such as degradation of insulation material or other portions of electriccomponents in the equipment, turn-to-turn shorts in coils, overloading,loose connections, or the like, various diagnostic theories have beendeveloped for correlating the quantities of various gases in fluid withparticular faults in electrical equipment in which the fluid iscontained. However, since conventional methods of off-line DGA requireremoval of fluid from the electric equipment, these methods do not, 1)yield localized position information relating to any fault in theequipment, 2) account for spatial variations of gases in the equipment,and 3) provide real time data relating to faults. If analysis isconducted off site, results may not be obtained for several hours.Incipient faults may develop into failure of the equipment over such aperiod of time.

The measurement of hydrogen gas in the oil of an electrical transformeris of interest as it is an indication of the breakdown of the oil causedby overheating and/or arcing inside the transformer. Transformer oilcools the transformer and acts as a dielectric. As transformer oil agesit becomes a less effective dielectric. The increase in hydrogendissolved in the transformer oil is an indicator of the coming failureof the transformer.

For large transformers there are hydrogen sensors that use gaschromatography or photo-acoustic spectroscopy to determine the amount ofhydrogen gas within a transformer's oil. Such devices are very expensiveand the expense is not justified for smaller transformers. There aremany older, small transformers that could be monitored if a low-costmethod of doing so was available.

A lower-cost gas monitor, the Hydran™ M2 manufactured by GeneralElectric Company has been in use. However, this gas monitor only sensescombustible gases and then uses a formula to estimate how much of thegas typically is hydrogen and how much is other gases.

An article “Overview of Online Oil Monitoring Technologies” by TimCargol at the Fourth Annual Weidmann-ACTI Technical Conference, SanAntonio 2005 provides a discussion of oil gas measuring techniques,including hydrogen measurement.

Palladium hydrogen sensors are disclosed in Gases and Technology,July/August 2006, in the article, “Palladium Nanoparticle HydrogenSensor” pages 18-21. Palladium sensors are also disclosed in U.S. PatentPublications 2007/0125153-Visel et al., 2007/0068493-Pavlovsky, and2004/0261500-Ng et al. U.S. Patent Application No. 2010/007828 disclosesa hydrogen sensor for an electrical transformer.

There is a need for low-cost method of determining hydrogen gas contentin oils, such as in electric power generation and transmission anddistribution equipment especially transformers. There is a particularneed for a method and apparatus for mounting a hydrogen sensor toelectric power generation transmission and distribution equipment thatdoes not require taking the equipment out of service and preferably usesexisting fittings or ports in the equipment without the necessity ofmaking new openings in the housings for the equipment. It wouldparticularly advantageous to provide a method and apparatus forattaching a hydrogen sensor to a transformer or the like using the portused for a pressure sensor especially a rapid pressure rise sensor.

BRIEF SUMMARY OF THE INVENTION

The invention provides a sensor assembly for determining theconcentration of hydrogen in an insulating fluid in electric powergeneration, transmission, and distribution equipment. The assemblyincludes a housing having an opening therein communicating with thefluid, a hydrogen sensor disposed in the housing and responsive to theconcentration of hydrogen in the fluid and generating a signal relatedto the concentration of hydrogen, and a pressure sensor disposed in thehousing responsive to the fluid and generating a second signalindicative of the pressure of the fluid in the equipment. The assemblyfurther includes a signal processor disposed in the housing andconnected to the hydrogen sensor and the pressure sensor and responsiveto the first and second signals for generating a third signalrepresenting the concentration of hydrogen in the fluid.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view of a transformer indicating possible locations for theattachments for sensors.

FIG. 2 is a view of a transformer indicating a location on thetransformer.

FIG. 3 is a top view of the sensor housing shown in FIG. 2.

FIG. 4 is a prospective view of the housing for sensors.

FIG. 5 is a cross-section of the invention housing with sensorsinstalled.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides numerous advantages over prior apparatus. Theinvention is smaller, easily installed, and lower in cost than otherhydrogen sensing devices. The device is accurate and can be easilyretrofitted onto existing transformers or engines. The device provides avery accurate hydrogen sensor with real time results as removal of fluidis not required. The device allows replacement of the sensor withoutproviding a significant opening for oil to leave the container. Theinvention sensor utilizes instrument controls that are well known andavailable. These and other advantages will be apparent from thedescription below.

The invention provides easy retrofit of the hydrogen sensor to thetransformer as an opening in the transformer housing is already present.This also is lower in cost than if a new inlet to the transformer neededto be installed. Further, the installation of the invention is lowmaintenance and will work at higher temperatures such as 120° C.

Illustrated in FIG. 1 is a transformer 10. The transformer 10 isprovided with pressure relief devices 14 and 16. The transformer 10 ispartially cutaway to show the coils 18. The transformer 10 has atemperature gauge 24. The temperature gauge 26 measures the temperatureof the oil of the transformer. The pipe terminal 28 connects to theoverflow pipe leading from pressure relief device 14. The optical fiberentry 32 provides direct reading of the winding temperature. A coolingtower 34 is utilized to regulate the temperature of the oil in thetransformer by cooling when necessary using fans 36. The drain valve 38is utilized to drain the oil for changing or to secure test samples.Electromechanical thermometers 42 sense the temperature of the oil inthe transformer. The IED intelligent electronic device 44 controls thesensing devices and provides readouts of the information sensed. Itfurther may control the cooling of the reactor as necessary. A rapidpressure rise relay 46 is also provided on the transformer. A flowgauge, not shown may be provided at location 48. The various temperatureand pressure sensors, pressure release devices, drains, and flow gaugesmay provide mounting areas for hydrogen sensors.

FIG. 2 shows a transformer 10 having a hydrogen sensor housing 13mounted on flange 46 of the transformer 10. The housing 13 is attachedto the flange 46 by way of shutoff valve 58. The valve may be turned offby knob 62. FIG. 3 is a top view of the hydrogen sensor housing 13.

FIG. 4 is an exploded perspective illustration of the housing 13 asmounted onto a transformer, by way of a shutoff valve 58. The flange 64provides access to the transformer through the shut off valve 58. Asillustrated in FIG. 4 the sensors are not present. The housing element13 contains a semiconductor element 12 for measuring hydrogenconcentration in an insulating fluid in electric power generationtransmission and distribution equipment. The mounting flange 14 has aplurality of bolt holes 16 and provides access to the interior of thetransformer equipment and provides a plurality of bolt receivingopenings 16 arranged on the mounting flange 14 in a first pattern. Thefirst flange 18 has one or more openings for receiving one or moresemiconductor hydrogen sensors and an outside periphery. The firstflange is also provided with a plurality of bolt receiving apertures(not shown) that correspond to the bolt pattern 16 of the mountingflange 14. A second flange 23 having a second plurality of boltreceiving apertures corresponding to the first pattern and the boltholes within the periphery of the second flange is provided as the endof the housing element 13. The housing body 13 has the bolt apertures inthe second flange 23 disposed a sufficient distance from the housing toallow access for bolts (not shown) to be disposed in the apertures forinserting and removing the bolts from the apertures and the secondflange has an outer periphery contained within the outer periphery ofthe first flange.

The housing is provided with at least one wire receiving opening 26extending from the housing body 13 at the expanded end 38. A cover 28 isprovided for closing the end of the housing body distal from themounting second flange 23. The first seal 32 is disposed between thefirst and second flanges. The first seal provides sealing around the oneor more sensor receiving openings 42 and 44 and the valve opening of thesampling or bleeding valve 36. A second seal 32 is disposed on the firstflange for engaging the mounting flange. The second seal surrounds andseals the sensor receiving openings 42 and 44 when sensors are inserted.A sampling or bleeding valve 36 is disposed on the first flange incommunication with the interior of the equipment and oriented so thatwhen opened trapped gas will exit the valve. A cap 35 for the valve 36is provided. The sampling valve extends to an edge of the flange 18 andcommunicates with the inner surface of the flange opposite the housingbody.

The housing 13 comprises an expanded end 38 on the end opposite to thesecond flange. It is noted that sensor opening 44 is generally in thecenter of and perpendicular to the first flange. The second opening 42is somewhat to the side and is threaded at an oblique angle to theflange to provide more clearance for the second sensor. The obliqueangle also permits any trapped air to move from the tip of the pressuresensor to the bleed valve.

FIG. 5 shows the sensor assembly with a detector 46 for hydrogen ininsulating fluid in electric power generation, transmission, anddistribution equipment installed in a housing such as in FIG. 4. Thehydrogen sensor is responsive to the concentration of hydrogen in thefluid and generates a signal related to the concentration of hydrogen. Apressure sensor 28 is also disposed in the housing and is responsive tothe fluid and generates a second signal indicative of the pressure ofthe fluid in the equipment. A signal processor 66 is in the housing andconnected to the hydrogen sensor, and the pressure sensor. The signalprocessor 66 is responsive to the first and second signals forgenerating a third signal representing the concentration of hydrogen inthe fluid.

The sensor assembly comprises a tube 52 threaded into the threadedopening 44 of the first flange 18. The hydrogen sensor 46 is disposed inthe tube 52. The second threaded opening 42 has a pressure sensor 48threaded into the opening 42.

The sensor assembly and housing that accepts two sensors is particularlydesirable as two sensors are placed onto one flange of the transformer,power generator other electrical equipment. Generally, in sensinghydrogen in a gas there is a need to know the gas pressure of the fluidin order to do a known calculation to determine the percentage ofhydrogen present. If the hydrogen sensor is in oil, pressure is notneeded to calculate hydrogen content of the oil. The placement of twosensors in one housing on one flange is a compact method of obtainingtwo measurements. While illustrated with the hydrogen compositioncalculation being done in the sensor housing it is also possible thatthe IED central control unit could do the calculation and provide thereading. Having the hydrogen sensor immediately adjacent the pressuresensor allows better accuracy than if the two sensors are in the airspace.

The entire unit can also be used in the gas space in sealedtransformers, not just under oil, and it is where the pressuremeasurement is in the gas space that the pressure sensor, in combinationwith the hydrogen sensor, would do double duty to allow calculation ofhydrogen concentration as well as measure rapid pressure rise.

As is apparent from the drawings the placement of the first flange 64,between the mounting flange 14 of the shut off valve 58 allows placementof the oxygen sensor without the formation of an additional hole in thetransformer. The location of the rapid pressure release device 46 at theside of the transformer allows sampling of hydrogen in the transformeroil rather than in the open space above the liquid coolant. Otherlocations also would place the hydrogen sensor in the liquid coolant.Sensors are known for sensing hydrogen in liquid as well as in gas andselection of the proper sensor would be within the skill of the artdepending upon what type of transformer is utilized and the level of thetransformer oil. It is noted that for accurate sensing of the hydrogencontent oil or gas that the pressure of the oil or gas also needs to besensed.

The sampling valve 36 extends through an edge of the first flange 18 andcommunicates with a surface of the flange opposite the housing body andcommunicates with an opening exposed to the interior of the transformerequipment through the mounting flange 64.

Palladium containing hydrogen sensors and controllers for the sensorsare known in the art. Such sensors are disclosed in United States PatentPublication Nos. 2007/0125153-Visel et al. and 2007/0240491-Pavlovsky,hereby incorporated by reference. An article in Gases and Technology,July/August 2006 “Palladium Nanoparticle Hydrogen Sensor” by I.Pavlovsky, also contains a description of hydrogen sensors and themethods and apparatus for their use. The palladium nanoparticlesutilized in these preferred sensors for the invention are intrinsicallysensitive to hydrogen and sensors based on palladium nanoparticlenetworks do not produce false alarms in the presence of other gases.This makes them particularly desirable for use in the devices of theinvention as other gases may be present when the hydrogen is sensed.Other hydrogen sensors and their controllers are disclosed in U.S.Patent Publication Nos. 2007/0068493-Pavlovsky and 2007/0240491-Pavloskyet al., also incorporated herein by reference. The preferred hydrogensensor for the instant invention is a semiconductor palladium-typesensor because it provides good performance in the transformerenvironment.

While the drawings illustrate the attachment of the hydrogen, sensingdevice to the rapid pressure release device this mounting method couldbe utilized at other locations on the transformer where there is aflange opening and space for the hydrogen sensor. Other locations toconsider would be on the load tap changer 22 and the drain valve 38.

The invention has been described in detail with particular reference toa presently preferred embodiment, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention. The presently disclosed embodiments are thereforeconsidered in all respects to be illustrative and not restrictive. Thescope of the invention is indicated by the appended claims, and allchanges that come within the meaning and range of equivalents thereofare intended to be embraced therein.

1. A sensor assembly for determining the concentration of hydrogen in aninsulating fluid in electric power generation, transmission, anddistribution equipment comprising: (a) a housing having an openingtherein communicating with the fluid; (b) a hydrogen sensor disposed inthe housing and responsive to the concentration of hydrogen in the fluidand generating a signal related to the concentration of hydrogen; (c) apressure sensor disposed in the housing responsive to the fluid andgenerating a second signal indicative of the pressure of the fluid inthe equipment; and; (d) a signal processor disposed in the housing andconnected to the hydrogen sensor and the pressure sensor and responsiveto the first and second signals for generating a third signalrepresenting the concentration of hydrogen in the fluid.
 2. The sensorassembly of claim 1, in which the housing comprises a flange having afirst threaded opening therethrough.
 3. The sensor assembly of claim 2,in which the housing comprises a tube threaded into the opening.
 4. Thesensor assembly of claim 3, in which the hydrogen sensor is disposed inthe tube.
 5. The sensor assembly of claim 2, comprising a secondthreaded opening in the flange.
 6. The sensor assembly of claim 5, inwhich the pressure sensor is threaded into the second opening.
 7. Thesensor assembly of claim 2, comprising a sampling valve extendingthrough the housing in communication with the insulating fluid.
 8. Thesensor assembly of claim 7, in which the sampling valve extends througha sidewall of the flange.
 9. The sensor assembly of claim 8, in whichthe sampling valve communicates with a valve opening exposed to theinterior of the equipment.